Characteristics of thin lanthanum lutetium oxide high-k dielectrics

In this work, we evaluate the thermal stability of thin film lanthanum lutetium oxide (LLO) on silicon deposited using molecular beam epitaxy (MBE). Thin LLO films are capped with TaN and annealed at 700 °C or 900 °C in nitrogen or oxygen ambients. SIMS analysis indicates no La and Lu up diffusion into TaN after annealing. However, after a 900 °C anneal Si is detected in the LLO. SIMS data also suggested growth of interfacial oxide upon anneal. Cross sectional TEM of as deposited films show a sharp high-k/Si-substrate interface with very thin interfacial layer. An increase in the LLO layer thickness, and the interfacial layer thickness between the LLO and the Si-substrate is observed after annealing. Capacitors with LLO dielectrics were also formed using TiN electrode and low leakage is demonstrated for samples annealed at 700 °C. However, a large positive flatband voltage shift and an increase in leakage is observed in LLO capacitors after undergoing 900 °C anneal with a TiN metal gate.